Questions About Future Volcanic Activity at Yellowstone

Is it true that the next caldera-forming eruption of Yellowstone is
overdue?

No. First of all, one cannot present recurrence intervals based on only two
values. It would be statistically meaningless. But for those who insist... let's
do the arithmetic. The three eruptions occurred 2.1 million, 1.3 million and
0.64 million years ago. The two intervals are thus 0.8 and 0.66 million years,
averaging to a 0.73 million-year interval. Again, the last eruption was 0.64
million years ago, implying that we are still about 90,000 years away from the
time when we might consider calling Yellowstone overdue for another caldera-
forming eruption. Nevertheless, we cannot discount the possibility of another
such eruption occurring some time in the future, given Yellowstone's volcanic
history and the continued presence of magma beneath the Yellowstone caldera.

When will Yellowstone erupt again?

We do not know. Future volcanic eruptions could occur within or near Yellowstone
National Park for the simple reason that the area has a long volcanic history
and because there is hot and molten rock, or magma, beneath the caldera now.
Yellowstone is monitored for signs of volcanic activity by YVO scientists who
detect earthquakes using seismographs and ground motion using GPS (Global
Positioning System). YVO has not detected signs of activity that suggest an
eruption is imminent.

The crust of North America continuously moves southwest over the Yellowstone
hotspot as the Earth's crust stretches above it, promoting the ascent of heat
and molten rock. These processes produce basalticmagmas within the Earth's
mantle, which rise into the overlying crust and continue to heat the rocks
beneath Yellowstone, maintaining and possibly adding to the rhyolitemagma in
the crust above.

Yellowstone's 2-million-year history of volcanism, the copious amount of heat
that still flows from the ground, the frequent earthquakes, and the repeated
uplift and subsidence of the caldera floor also testify to the continuity of
magmatic processes beneath Yellowstone and point to the possibility of future
volcanism and earthquake activity.

What type of eruption will occur if Yellowstone erupts again?

Yellowstone's volcanic and hydrothermal history suggests the potential for
various kinds of eruptions in the future. The likelihood of a certain type of
eruption occurring in the future can be judged by how often eruptions have
occurred in the past.

The most likely type of eruption would not be volcanic but, rather,
hydrothermal. This type of small, but still explosive eruption can occur from
shallow reservoirs of steam or hot water rather than molten rock. These
reservoirs are the sources of Yellowstone's famous geysers, hot springs, and
fumaroles. Such explosions could blast out shallow craters more than a kilometer
wide; as has occurred in the northern Yellowstone Lake Basin, including Mary Bay
and nearby Turbid Lake and Indian Pond, and in western Yellowstone National Park
north of Old Faithful. Each of these craters was produced by steam blasts within
the past few thousand years.

The most likely type of volcanic eruption at Yellowstone would produce lava
flows of either rhyolite or basalt; rhyolitic lava eruptions could also include
explosive phases that might produce significant volumes of volcanic ash and
pumice. Such eruptions could range in size from smaller than the 1980 eruption
of Mt. St. Helens through much larger than the 1991 Mount Pinatubo eruption.

The least likely but worst-case volcanic eruption at Yellowstone would be
another explosive caldera-forming eruption such as those that occurred 2.1
million, 1.3 million, and 640,000 years ago. However, the probability of such an
eruption in any given century or millennium is exceedingly low- much lower than
the smaller eruptions mentioned above.

Could a large Yellowstone eruption significantly change weather patterns?

If another catastrophic caldera-forming Yellowstone eruption were to occur, it
quite likely would alter global weather patterns and have enormous effects on
human activity, especially agricultural production, for many years. In fact, the
relatively small 1991 eruption of Mt. Pinatubo in the Philippines was shown to
have temporarily, yet measurably, changed global temperatures. Scientists,
however, at this time do not have the predictive ability to determine specific
consequences or durations of possible global impacts from
such large eruptions.

Can you release some of the pressure at Yellowstone by drilling into the
volcano?

Scientists agree that drilling into a volcano would be of questionable
usefulness. Notwithstanding the enormous expense and technological difficulties
in drilling through hot, mushy rock, drilling is unlikely to have much effect.
At near magmatic temperatures and pressures, any hole would rapidly become
sealed by minerals crystallizing from the natural fluids that are present at
those depths.